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RedHat 9 (Linux i386) - man page for pnmrotate (redhat section 1)

pnmrotate(1)			     General Commands Manual			     pnmrotate(1)

       pnmrotate - rotate a portable anymap by some angle

       pnmrotate [-noantialias] angle [pnmfile]

       Reads a portable anymap as input.  Rotates it by the specified angle and produces a porta-
       ble anymap as output.  If the input file is in color, the output will be too, otherwise it
       will  be grayscale.  The angle is in degrees (floating point), measured counter-clockwise.
       It can be negative, but it should be between -90 and 90.  Also, for rotations greater than
       45  degrees you may get better results if you first use pnmflip to do a 90 degree rotation
       and then pnmrotate less than 45 degrees back the other direction

       The rotation algorithm is Alan Paeth's three-shear method.  Each shear is  implemented  by
       looping	over the source pixels and distributing fractions to each of the destination pix-
       els.  This has an "anti-aliasing" effect - it avoids jagged edges and  similar  artifacts.
       However,  it also means that the original colors or gray levels in the image are modified.
       If you need to keep precisely the same set of colors, you can use the  -noantialias  flag.
       This  does the shearing by moving pixels without changing their values.	If you want anti-
       aliasing and don't care about the precise colors, but still need  a  limited  *number*  of
       colors, you can run the result through ppmquant.

       All flags can be abbreviated to their shortest unique prefix.

       "A  Fast Algorithm for General Raster Rotation" by Alan Paeth, Graphics Interface '86, pp.

       pnmshear(1), pnmflip(1), pnm(5), ppmquant(1)

       Copyright (C) 1989, 1991 by Jef Poskanzer.

					 12 January 1991			     pnmrotate(1)

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